Optical navigation is an intuitive and precise way to track moving objects. The optical approach is intuitive because our own human stereo vision system calculates object locations and trajectories by optical triangulation. The precision of optical navigation is due to the very short wavelength of electromagnetic radiation in comparison with typical object dimensions, negligible latency in short distance measurements due to the extremely large speed of light and relative immunity to interference.
Optical navigation typically employs several cameras to determine the position or trajectory of an object in an environment by studying images of the object in the environment. Such optical capturing or tracking systems are commonly referred to as optical motion capture (MC) systems. In general, motion capture tends to be computationally expensive because of significant image pre- and post-processing requirements, as well as additional computation associated with segmentation and implementation of algorithms, see for example U.S. Pat. No. 6,324,296 to McSheery.
Low-cost portable computing devices such as handheld or palm-sized computers can support local communication between nearby computers, or more generally can support wireless network or internetwork communications. Users equipped with suitable portable computers can, for example, exchange e-mail, browse the web, utilize mapping software, control nearby computer peripherals (e.g. printers), or receive information from local devices (e.g. job status of a printer). The flexibility and utility of various applications can be enhanced if the precise spatial location of the portable computing device is known. Knowing the location of the portable computing device (with a precision of several meters to less than 1 meter, or so) permits construction of user specific maps, transfer of location information to others, and receipt of location information for nearby computational or real world resources (e.g. answering such questions as “where is the nearest printer” or “where is the nearest coffee shop”). For this reason, having easily determinable and reliable position information would be a useful feature.
However, spatial localization with low cost devices can be difficult. Devices incorporating GPS receivers often do not work indoors because of poor radio reception and can require a substantial amount of time to determine position with a required accuracy. In many areas, there may not be any differential GPS availability to gain the necessary meter level precision for greatest utility. Other wireless schemes for localizing spatial position are generally not sufficiently precise (e.g. digital cellular telephone service areas with 1000 meter errors), or too expensive (inertial navigation systems).
It would be desirable to provide a novel approach to location sensing to overcome at least some of the drawbacks of known techniques, or at least that provides a useful alternative.